Circuit checking apparatus



Jan. 13, 1953 c. M. HINES CIRCUIT CHECKING APPARATUS Filed Aug. 22, 1950 Patented Jan. 13, 1953 CIRCUIT CHECKING APPARATUS Claude M. Hines, Verona, Pa., assigner to Westinghouse Air Brake Company, a corporation of Pennsylvania Application August 22, 1950, Serial No. 180,809

11 Claims. l

This invention relates to circuit checking apparatus and more particularly, to apparatus adapted to be associated with control circuits of electro-pneumatic brake control systems, employed on a train of cars, for the purpose of selectively signalling integrity or lack of integrity of the said control circuits and accompanying electrical devices at all times.

The modern electro-pneumatic brake system for a train of cars, embodies a plurality of control circuits which extend throughout the length of the train from car to car, on which circuits operate brake control magnet valves located on each car. These magnet valves, of which there are usually two on each car, are called the application magnet valve and release magnet valve, respectively, and are controlled by a common electro-pneumatic controller, called the master controller, which is normally located on the locomotive.

Various systems and methods have been employed for checking and indicating the integrity condition of the control circuits and associated magnet valves and electrical devices. One of such systems is described in United States Patent No. 2,573,442, issued October 30, 1951, which is assigned to the assignee of this invention.

The said Patent No. 2,573,442 discloses a checking and indicating apparatus which when used in conjunction with electro-pneumatic brake control system, enables a check of the integrity condition to be made of the control circuits and associated electrical devices, and also indicates such integrity condition to the train engineer.

In the above-mentioned application, an integrity check is made of both the application control circuit and the release control circuit by use of a Wheatstone bridge arrangement for each circuit, while the train brakes are released; and, while the train brakes are applied, an integrity check is made of the release control circuits by use of a current-responsive relay 'in the circuit. However, although such checking and indicating scheme satisfactorily checks and indicates the integrity condition of both the application control and release control circuits while the train brakes are released, it checks only the release control circuit and not the application control` Ycircuit while the train brakes are applied. Also, :ln the system disclosed in the said application,

'if a fault occurs in the release control circuit the instant immediately after application of the brakes is initiated, during which time .both conitrol circuits are energized simultaneously, the ifa-1i will s0 undetected until .the .nesta Con- 2 troller is restored to lap or brake release position.

It is an object of the present invention to provide an improved circuit checking system of the type disclosed in the above-mentioned pending application, characterized in that it includes means for checking the integrity of the control circuits and the associated electrical apparatus in such a manner as to indicate the occurrence of a fault in both the application and release control circuits not only while the brakes are released, but also during a brake application.

It is another object of my present invention to provide an improved circuit checking apparatus of the type referred to in the foregoing object and further characterized in that it includes means for checking the integrity of both the application and release circuits during brake application immediately upon initiation of such a brake application; and also during release of the brakes immediately upon initiation of such a brake release after a brake application.

The above objects together with other objects which will be made apparent in the subsequent description of my invention, are obtained by apparatus to be hereinafter described when read in connection with the accompanying drawings wherein the single figure depicts a simplified diagrammatic view of a circuit-checking and indicating apparatus as applied to the circuits of a simpliiied electric brake control system.

In the drawing, the simplified electric brake control apparatus comprises a source of direct current voltage, such as a battery I, a supply wire 2, and a return wire 3, a master controller device shown herein as a two-pole master switch 4 having an application contact 5 and a release contact 6, the contacts 5 and 6 being connected respectively to the application wire I and the release wire 8 which extend throughout the train and to which are respectively connected the application magnet 9 and the release magnet I0 on each car of the train, and a common return wire Il.

It can be seen from the drawing that when switch 4 is positioned so that neither of its contact members are closed, a position referred to as the brake release position, the circuit to the magnets 9 and l0 is incomplete. When the switch 4 is positioned so that both contacts 5 and B are closed, a position referred to as the application position, both magnets 9 and l0 are energized. When only the release contactmember B is closed, a position referred to as the "lap position is deiined in which the release magnets IB only will be energized.

The circuit checking and indicating apparatus shown in the drawing is in simplified form and comprises a casing or panel I2 within which or to which are attached a single winding relay I3, a two-winding relay I4, a two-winding relay I5, and a single winding relay I6, each of these relays having contact members for interrupting or completing circuits which are described hereinafter.

This apparatus also comprises several indicating devices such as a bell or buzzer I1, an allclear lamp I8, and a fault lamp I9 which operate in conjunction with the previously mentioned relays.

A bridge and coding cabinet 2B is shown which contains the Wheatstone bridge arrangements (not shown) and the coding arrangements (not shown) for checking the integrity of the control circuits during release as described and shown in detail in the previously mentioned Patent No. 2,573,442. For simplicity, this portion will be shown and described only as the cabinet 2i! which functions to check the integrity of the control circuits during release and to supply a `pulsating voltage from the vbattery supply I to a coding wire 2I, which if so desired, may be more fully understood by reference -to the mentioned pending application.

The checking and indicating apparatus also includes a push-button switch 22, a double-pole single-throw switch 23, and various wires, resistors and condenser connected and functioning as described hereinafter.

When the switch l is in its open or brake release position, the circuit checking apparatus operates as follows:

The operator first closes the switch 23 which establishes a circuit from the battery l by way of the battery supply wire 2 to a terminal post 2d in the casing I2, a contact member 25 of the switch 23, a vB-lwire 2S, a wire 27, a current limiting resistor 28, a wire 29, the lower Vwinding 3U of relay It, a wire 3|, a wire 32, and a wire 33 to a B- terminal post 34, and thence to the battery I by way of battery return wire 3. The completion of this circuit causes the relay le to be energized t its picked-up position, thereby closing its contact members 35, 36, 3'! and 33 and moving Yits contact member 39 to its upper closed position. With the contact member 33 in its upper closed position, the operator now closes the push-button switch 22, which establishes a circuit for energizing the relay I3 to its picked-up position.

The circuit for energizing relay I3 is traced from wire 2I which is subject to a pulsating D. C. voltage supplied by the apparatus (not shown) included in the cabinet 219 (as will be vexplained presently) to the closed contact member 33 of relay I3, wire di), wire 4I, the closed switch 22, wire 42, wire 33, the winding .44 of relay I3, wire 35, B-V wire .46, the closed contact member il? .of the switch 23, wire 48, and wire 33, to the B- terminal post 34 and thence to the battery I by way of the battery return wire 3. The bridge and coding apparatus in the cabinet 23 operates to supply the mentioned pulsating D. C. voltage to wire 2l in response to energizati-on of circuits from the battery I. These circuits may be traced from the battery I by way of the battery supply wire 2, wire 2a, through the bridge and coding apparatus in the cabinet 2B, wires 5S and 63 .and

the contact members 35 and 35 of relay I4 and wires 60 and 57 to the respective application and release wires 'I and 8 and thence through the respective control circuits to the common return wire I I, terminal post 63, wire S4, resistor 35, Wire 33 and B- terminal post 34 and the battery return wire 3 to the battery I.

As explained in the mentioned pending application the bridge and coding apparatus continues to operate to supply the said pulsating D. C. voltage to wire 2I as long as no fault exists in the control circuits.

The completion of the circuit for energizing relay I3 causes the relay I3 to be actuated to its picked-up position, thereby causing its contact members 9 and 50 to move to their upper closed positions, and its contact member 5l to move to its closed position. With the contact 5I of the relay I3 closed, the operator may new open the switch 22, thereby permitting the relay i3 to maintain its own stick circuit through the closed contact 5I which parallels switch 22 in the energizing circuit previously traced.

Connected in parallel with the winding i3 ci relay I3 and energized simultaneously therewith is a circuit including wire 52, a resistor wire 51E, condenser 55, wire 5S, wire 5l, the closed Contact 38 of relay I3, and wire 58 to wire This circuit makes up a loop circuit with the winding 44 of relay I3 and serves to maintain the relay I3 energized for a short period of time by discharge of condenser 55 after the energ circuit described in a previous paragraph is interrupted, for reasons Vtobe described hereina'ter,

The relay I3 remains energized in its pickedM up position While the brakes are released so long as the bridge and coding equipment in the cabinet 2i? delivers pulsating voltage of a certain irequency to the wire 2i, which it will do while the integrity of the application and release control circuits are unimpaired. These control circuits are connected to the cabinet 2Q in brake release respectively by way of wire 58 the closed contact member 35 of relay I4, wire 58, application ter-v minal post BI, wire 62, application wire i, and the application magnets 9 to the common return wire II which can be traced to the battery return wire 3 by way of terminal post wire 53, resistor S5, Wire 33 and B terminal post and by way of wire 3S, closed contact member 33 of relay Ill, wire 6l, release terminal post wire 53, release wire 8, and in parallel through the release magnets I3 to the common return wire Il, which can be traced to the battery return wire 3 and a similar wire iI which can be traced to the battery return wire 3 in a similar manner.

As long as relay I3 remains energized, the oontact member 50 remains in its upper closed position, thus completing a circuit for energizing the all-clear lamp I8, which circuits extend from the B+ wire 26, through contact member 53, wire l0, lamp i3, and wire 'H to the B- wire d3. However, ii for any reason the relay i3 becomes deenergized, the contact member 53 will assume its lower closed position and establish a circuit for energizing the fault lamp IQ, which circuit may be traced from the 'B+ Wire 23, by way ci contact member 3B, wire l2, lamp is, and wire 'i3 to the B- wire 46. An explanation of these just described circuits will appear hereinafter'.

When the relay I3 is energized, the Contact member i9 is effective in its upper closed position to establish a circuit which may be traced from the B+ wire v2.? 'by way of Wire lli, contact niember 43, wire closed contact member 3l of relay I 4, wire 7S, the lower `winding 'Il of the relay i3,

wire 18, current limiting resistor 19, and wire 80 to the B- wire 46. The energization of this circuit results in the actuation of the relay I5 to its picked-up position, thereby causing the contact members 8l and 82 to move to theirrespective closed positions for purposes applicable during brake application as will be explained hereinafter. If for any reason the relay I3 becomes deenergized, the contact member 49 will assume its llower closed position, thus completing a circuit for energizing a buzzer I 1 by way oi the B-I- wire 25, wire 14, contact member 4Q, wire 83, buzzer I1, and wire 84 to the B- wire 46 for a purpose described hereinafter.

The circuits described thus far, with but `a few exceptions, are in use during the normal conditions of the circuit checking and signalling with the brakes released (switch 4 open with both contacts 5 and 6 open) and no fault existing in the battery supply or in the control circuits.

The circuit checking and signalling apparatus operates during a brake application as follows:

Assuming no faults are present, the brakes are applied by operation of the master controller device or switch 4, in the usual manner. As can be seen from the drawing, operation of said switch 4 causes the release contact 5 to be closed an instant or so before the application contact 5 is closed. When the release contact 6 is closed, a circuit is completed for energizing the release magnets by way of the release wire 8, the parallel connected release magnets 9, the common return wire I I, terminal post 63, wire 64, resistor 65, wire 33 and B terminal post 34 to the battery return wire 3. cuit is energized by utilizating the voltage-drop across the potentiometer resistor 55, said circuit being in parallel with the resistor 95 by connection to wire E4 and including a wire 85, a currentlimiting resistor 85, an adjustable resistor 81 which is varied according to train length as will be explained later, a wire 5S, the upper winding S9 of relay I5 and wire 99 to wire 33. Also in parallel with the resistor 65 are two variable resistors 9I and 92 adjusted to a predetermined value for varying the voltage-drop across resistor 55. The adjustable resistor 31 is so adjusted for a particular train length and thus for a corresponding number of magents in the release control circuit that with no faults in the release control circuit, the current delivered to the windling 89 el relay i5 is just sufficient to maintain the relay I5 picked-up. However, when a fault occurs in the release control circuit, the current delivered to said winding of said relay is insufficient to maintain relay I5 picked-up.

Simultaneously with the energization of the release control circuits, a circuit is completed for energizing the top winding 54 of relay i4 from the release wire i by way oi wire 59, release terminal post 58, Wire t1, wire 93, winding .94 of relay I4, wire 32, wire 33, B- terminal post to the battery return wire it will be noted that the bottom winding of relay I 4 is also energized as was previously described, but the energize-tion of the top winding 5 4 opposes the energization of the bottom winding. The opposing energization of the two windings causes the relay I4 to be returned to its dropped-out position in which the contact members 35, 36, 31 and 1:25 are opened and the contact member 35! is moved to its lower closed position.

When the contacts 35 and 39 are restored to their open position, the circuits connecting the bridge arrangements in the cabinet 29 to the con- As this circuit is completed, another cirtrol circuits are interrupted, thus causing the bridge and coding equipment in the cabinet 20 to discontinue the supply of pulsating D. C'. voltage to the Wire 2 I.

The contact member 38 of relay I4 is effective when moved to its lower closed position to establish a circuit for maintaining the relay I3 in its picked-up position, which circuit extends from the B+ wire 25, by way of wire 95, the closed contact member 82 of relay l5, wire 95, contact member 39, wire 4G, contact member 5I of relay I3, wire 42, Wire 43, the Winding 44 of relay i3 and wire 45 to the B- wire 45. During the interval in which the contact member 39 moves from its upper closed position to its lower closed position, the relay I3 is maintained energized by the current discharging from condenser 55 through the loop circuit including wire 54, resistor 53, wire 52, wire 43, the winding 44 oi relay I3, wire 45, wire 53, the contact member 8| of relay I5 and wire 56.

Contact member 31 is effective when restored to its open position to interrupt the circuit previously described for energizing the lower winding 11 of relay I5, thus deenergizing the lower Winding of relay I5. However, as previously described, the relay I5 will not drop-out because the upper winding 89 will remain energized and thereby maintain the relay in its picked-up position as lon: as no fault exists in the control circuits.

Contact member 33 is eiective, when opened to interrupt the loop circuit giving the time delay to relay I3 before dropping-out as previously discussed, with the result that drop-out of relay I3 will occur without delay if the relay I5 drops out due to a fault occurring on the control circuits while the brakes are applied.

An instant after the closing of the release contact 6 of the master controller or switch device 4, the application contact 5 is closed for energizing the application magnets 9. Closing of the application contact 5 establishes a circuit for energizing the winding 98 of relay I6 which is thereby actuated to its picked-up position, this circuit being traced from the application wire 1, wire 62, the application terminal 6I, wire G0, wire 91, the winding 98 of the relay I6, wire 99, B- wire 45, the contact member 41 of the .switch 23, wire 48, Wire 33, B- terminal post 34 and the battery return wire 3. Upon energization of relay I6 the contact member |90 of said relay is moved to its closed position thus completing a shunt circuit across the winding 83 of relay I5. This shunt circuit, which includes a wire IilI, contact member |00 of relay I5, variable resistor I02, and wire 133, decreases the effective ampere turns of the winding .80 by shunting current from winding B9. However, due to the increased current supplied to energize the application magnets 9, the current through winding 89 will be maintained at a degree sufficient to keep relay I5 picked-up, unless a fault occurs on either the application or the release control circuits. The circuit for energizing the application magnets 9 is completed by way of the application wire 1, the magnets 9, the common return wire II, terminal post 63, wire E4, resistor 65, wire 33, B- terminal post 34, and the battery return wire 3. Thus the sum of the currents in the release control circuit and in the application control circuit produces voltagedrop across the resistor E5. The winding 89 of relay I5 being connected in parallel with the resistor 55 is thus subject to the greater voltagedrop across resistor 65 to maintainv the current through winding 89 equal to the current existing when the shunt circuit across winding 89 is not established. In 'this manner, the relay I5 is maintained 4picked-'up vwhile both the application control circuits and the `release control circuits are energized, unless a fault occurs in either control circuit, in which'case the/current through the winding 89 is decreased sufficiently to effect a drop-out of relay I5.

When the application control circuit is again deenergized while the release control circuit remains energized, yconsequent upon automatic return of the master switch 4 to its lap position, the relay I6 simultaneously drops-out due to interruption of Vthe described shunt circuit across windingg of relay I5, and the conditions existing then will be `as previously described when only 'the release control circuit is energized.

In view of the Vdescription of my invention thus far, an explanation ofthe operation of this apparatus when vthe master switch 4 is in each `of its respective operating conditions will follow, that is, in brake release (contacts 5 and 6 of switch 4 open), the initiation of a brake application (contacts closed and contact 5 open),

-:full application (both contacts v5 and closed),

lap position `(contact 6 closed and contact 5 open), and `release after application (both contacts 5 and 6 open).

In brake release position of the master switch 4, with no faults present on the control circuits, the lower winding 30 of relay I4 is energized to its picked-up posi-tion by voltage from the 'B+ wire 26 thus connecting the bridge and coding equipment in cabinet ZIl to the control circuits a-nd enabling a delivery of pulsating voltage to wire 2I. The relay I3 is energized to its picked-up position by the pulsating D. C. voltage from wire "2-l, thus completing a circuit for energizing the all-clear `lamp I8, and also cornplje'ting a circuit for energizing the lower winding TI of relay I5 to its picked-up position. Should a fault occur in either or both the application orv release control circuits, the corresponding bridge arrangements (not shown) in cabinet '20 became unbalanced and cease to supply pulsating voltage to Wire 2|, as explained rfully in Patent No. 2,573,442. With the supply 'ofvoltage to wire 2I interrupted the relay I3 would drop-out yand 'move contacts de and 50 to; their respective lower closed positions for completing Ycircuits for energizing` the buzzer Il 'and'ener'gizing the fault lamp I9 to indicate a iault tothe operator. After the fault has been found and corrected in the manner fully explained in my above mentioned pending applicar tion, the checking and indicating apparatus may be set lin operation again by closing the push button switch 22 which will again effect energization of relay I3 if the pulsating voltage supply has been restored to wire 2I.

AWhen a brake application is first initiated and only the release contact member 6 of the switch 4 is closed with `no faults present, the top winding 84 of the relay I4 is energized by voltage from the release wire 8, in opposition to the already energized lower winding 30, thus causing a droppingout of relay I4. Also, the upper winding 89 of relay I5 is energized by the voltage-drop across resistor 65 which is effected by the energization of all the release magnets I thus maintaining relay I picked-up. The dropping-out of relay i5 disconnects the control circuits from the bridge and coding 'equipment in case 20 at contact members 35 and 36 and thus effects an interruption of the pulsating voltage delivered to wire 2 I. The dropping-out of relay I4 also effects an interruption of the circuit for energizing the lower winding 11 of relay I5 at the v.contact member 3T, but, as Y previously mentioned, the upper winding 89 will maintain the relay I5 picked-up. The droppingout of relay I4 also moves the contact member 39 to its lower closed position to complete an alternate circuit for maintaining the relay I3 energized with Voltage supplied from B+ wire 26 and the contact 82 of relay I5. During the time in which the energizing voltage of relay I3 is being changed from the pulsating source on wire 2| to the battery supply Hon wire 26, the vcurrent discharging from 'condenser 55 will maintain the relay I 3 energized for a 'short time interval by way of the loop circuit previously described. Should a fault occur in the release control circuits in this short time interval in which only the release control circuit is energized upon initiation of a brake application, the voltage-drop across the resistor will decrease, resulting in a suliicient decrease in `the current Aenergizing the top winding 89 of relay I5 to allow the relay I5 to drop-out as previously explained. i With the dropping-out of relay I5, the circuit for energizing relay I3 will be interrupted thus dropping-out the relay I3 and moving the contact members 59 and 55 of relay I3 to their lower closed position to complete circuits for energizing the buzzer I'I and the lamp i5 to indicate the fault lto the operator.

When the brakes are applied and both the re- 1iease contact member 6 and the application contact member 5 of the switch areclosed, both the application and release circuits are energized.

1 The relays I3 and I4 remain energized in the same manner as 'described Ain the previous paragraph when only the release contact member 6 of switch i was closed. In addition, the relay I5 is energized to its picked-up position by voltage from the Vapplication wire 'I'. The upper winding of relay I5 .remains energized, but energized in this instance by the voltage-drop across resistor 55 effected not only by energization of all the release magnets I0 as in the previous paragraph, but by the voltage-drop across resistor effected by energization of all of both the release magnets I!! and the application magnets 9. This resulting increase in voltage-drop across resistor 55 causes an increase of current for energizing the winding 89 of relay I5 such that the current maintaining relay I5 picked-up is greater than that required. However, as relay I5 is also energized and picked-up, the contact member Id of said relay in closing completes a shunt circuit for bypassing this excess current through the winding 89 of relay I5 in such a manner that when no fault occurs on either control circuit, the current to the winding 89 is just suiiicient to maintain relay I5 picked-up. Should a fault occur on either control circuit, the current to winding 89 of relay I5 would decrease suiciently to allow relay I5 to drop-out, thus interrupting the circuit for energizing relay I3 and causing relay I3 to dropout. With relay I3 dropped-out, the contact members 49 and 5i) move to their respective lower closed positions, thus completing circuits for energizing buzzer I1 and lamp I9 to indicate a fault to the operator.

When the brakes have been applied and the master controller goes to lap position with the release 'contact member 6 closed and the application contact member 5 open again, the relay I will become deenergized because the application control circuit is deenergi'zed. The checking 'and indicating apparatus will thus again be conditioned exactly as it was described in the previous paragraph describing the condition of the apparatus when the brake application is first initiated with only the release control circuits energized.

When the master switch 4 is restored to brake release position from its brake application position, the top winding of relay I4 is deenergized allowing the energized lower winding 3u to cause the contact members of said relay to pick-up thus placing the bridge and coding cabinet 20 in the connected control circuits back in operation and supplying pulsating voltage for energizing relay I3 by Way of wire 2l. Also, the lower winding 'Il of relay I5 is again energized with the closing of contact member 31 of relay I4 before the top winding 89 is deenergized due to deenergization of the release control circuit. Relay I5 is thus maintained picked-up. Thus, the condition of the checking and indicating apparatus is returned to the conditions existing described in the previous paragraph for brake release.

It should be noted here that regardless'of the brake control position, if the battery supply circuit is interrupted, this faulty indication will be noted by the operator due to the fact that both the indicating lamp I8 and I9 will be deenergized.

It should be understood that while my invention has been disclosed speciiically in connection with two control circuits it is not limited in its operation to two control circuits, but may be adapted to operate with any number of control circuits.

Having n-ow described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. Apparatus for checking the integrity of a plurality of control circuits that are adapted to be selectively energized for eiecting diierent control functions, said apparatus comprising a iirst means for detecting the integrity of said circuits while they are deenergized, a second means for detecting the integrity of one circuit of said circuits While only said one circuit is energized, a third means for detecting the integrity of all of the circuits while all of said circuits are energized and means responsive to deenergization of all of the circuits to render said first means effective, and responsive to energization of one and of all of said circuits to render said second means and said third means effective, respectively.

2. Apparatus for checking the integrity of a plurality of control circuits that are adapted to be selectively energized for eiecting different control iunctions, said apparatus comprising a rst means for detecting the integrity of one circuit of said circuits while only said one circuit is cnergized, and means responsive to energization of another of said circuits for rendering said rst means effective also to detect the integrity or all of the energized of said circuits.

3. Apparatus for checking the integrity of a plurality of control circuits that are adapted to be selectively energized for effecting different control functions, said apparatus comprising integrity detecting means, and means responsive to energization and deenergization of a certain one of said circuits to selectively condition said detecting means to detect the integrity of one circuit of said circuits while only said one circuit is energized, and to detect the integrity of more than one of said circuits while such circuits are energized.

4. For use in connection with a plurality of control circuits adapted to be selectively energized for eiecting different control functions, ap-

paratus comprising a iirst means operative to detect the integrity of all of said circuits while all are deenergized, a second means operative to detect the integrity of one circuit of said. circuits while only said one circuit is energized, a third means operative to detect the integrity oi all of said circuits while all of said circuits are energized, signal means operable to indicate circuit integrity status, and means responsive to energization conditions of said control circuits to establish operative connection selectively between said signal means and said first means, said second means, and said third means.

5. Apparatus for checking the integrity of a plurality of control circuits that are adapted to be selectively energized for effecting different control functions, said apparatus comprising a rst means for detecting the integrity and lack of integrity oi' one circuit of said circuits while only said one circuit is energized, signal means operable by said rst means to indicate both circuit integrity and lack of circuit integrity, and means responsive to energization of another of said control circuits to render saidA rst means eiective to detect integrity and lack of integrity of all of the energized of said circuits.

6. Apparatus for checking the integrity and lack of integrity of two diierent circuits that are adapted to be selectively energized for a desired control purpose, said apparatus -comprising a rst means for detecting the integrity and lack of integrity of one circuit of said circuits while energized for control purposes, a second means for detecting the integrity and lack of integrity of the other circuit of said circuits while energized for control purposes, identical signal means controlled by said rst and said second means, for indicating the integrity and lack of integrity of either one or both of said circuits, and means responsive to energization and deenergization of one of said circuits for controlling the effectiveness of said first means and said second means.

7 For use in connection with two vehicle brake control circuits, the combination of a rst means for detecting the integrity of the brake control circuits while deenergized to effect release of the brakes, a second means for detecting the integrity of one circuit of said brake control circuits while energized to hold a brake application, la third means for detecting the integrity of both of said brake control circuits while energized to initiate a brake application, a iirst selecting means responsive to the energization of said one circuit to render said rst means ineiective and said second means enective, and responsive to the de-energization of said one circuit to render said first means eiiective and said second means ineffective, a second selecting means responsive t0 the energization of the other circuit of said brake control circuits to render said second means ineffective and said third means effective, and responsive to the de-energization of the said other circuit to render said third means ineffective `and said second means eiective.

8. Apparatus for detecting the integrity and lack of integrity of two control circuits having a common return wire and so arranged that one or both of said circuits are selectively energized, said apparatus comprising electro-responsive relay means adapted to remain picked up so long as it is energized by a current exceeding a certain value and dropped-out when the energizing current reduces below said value, and means responsive to energization and deenergization of one of said circuits for causing said electro-responsive relay' means to be energized in substantially the same degree above Vsaid certain yvalue for a nofault condition of one or both of" sfaid circuits Whether saidjone or both offsaid circuits are energized.

9. Apparatus for signalling the integrity and lack of integrity of twocontrol circuits, having a coinrnon return Wire and arranged so that one or both of said circuits are selectively energized, said apparatus: comprising electro-responsive relay means energized according to the current in said return wire, resistance means, a relay responsive to energization of one of said circuits for connecting. said resistance means in parallel with said electro-responsive relay means thereby to cause said electro-responsive relay means to dropout respons'ivelyto reduction of thev energizing current below' a certain val-ue incident to the ccc'urrence of a fault on saidv circuits Whether one or both of saidv circuits are energized.

l0. Apparatus forr checking the integrity status of a control circuit adapted to be selectively energized in a rst degree andin a greater degree, said control circuit including a plurality ofA controlled elements' connected electrically in parallel such that interruption inelectrical connection between said' elements will result in a decrease in current iicwing through said control circuit, said apparatus comprising relay means responsive to reduction in current below a certain value to establish a condition indicative of a faulty control circuit; rlieostatY means to regulate current from said control circuit insupply te. said. relay means suchv that' said current Will be in slight excess of saidV certain value whensaid control circuit is intact and energized in said nrst degree; resistance means adapted. toV be renderedeective to sfo limit current from said control circuit in supply to said relayine'ans as. to assure that said current will. remain in onlyslight excess of said certain value when. said control circuit is intactl and energized. in said greater degree; andlmeans responsive tovcnergization of. said control circuit insaid firstdegree and-.in saidgreater degree to. render saidresistance means ineiec- 4 l2 energy, a number of first electrical elements ccnnected ,in parallel, a number of second electrical elements connected in, parallel, a rst control Wire connected to the input to said iirst electrical elements,- al second control wire connected to the input tosaid second electrical elements, a return Wire connected to the output from both the 'rst and second electrical elements and also connected to thenegative terminator said source of electrical energy, and. operator's switch means operable selectively to connect to said source either said rst control Wire or both said; r'st control. Wire and said second control Wire,P o f rst resistance means connected in series with said return Wire, relay means having a connec tion. across said` resistance means to receive a certain proportion of. current from said return wire, said.) relay means being responsive. to a reduction in receipt of current via said donnee tion below a-certain value to establish acondition indicative of a faulty' control circuit, rheostat meansvin said connectionand in series With said relay means to so regulate current to said relay means such that said current Will bein slight excess of saidcertain value when the control'ecircuit is intact and said. rst control Wire only is connected. to said source; second` resistance means adapted` for a parallelconnection with said'. relay means to assure that current to said relay means will remain in onlyslight excess ci said. certain value When said 'second control Wire also` is connected to said source, and other relay means responsive to establishmentand disestablishment ofV current flow in saidsecond control wire to establish and disestablish, respectively,-` said parallel connection.

REFERENCES' CITED The following' references arer of'l recordl in the le of this patent:v

UNITED s'rirrnsv PATENTS Number Name Date 2,276,705 serese Mar. 1.7, 1942 2,478.000 Miller'- Au'g. 2 1949 

